Logging and monitoring boreholes has been done for many years to enhance and observe recovery of oil and gas deposits. In the logging of boreholes, one method of making measurements underground includes attaching one or more tools to a wireline connected to a surface system. The tools are then lowered into a borehole by the wireline and drawn back to the surface (“logged”) through the borehole while taking measurements. The wireline is usually an electrical conducting cable with command/synchronization/power/data transmission or “telemetry” capability. Similarly, permanent monitoring systems are established with permanent sensors that are also generally attached to an electrical cable.
In some seismic acquisition systems, a telemetry based seismic recorder sends commands and a timing or clock signal to remote acquisition units (e.g. nodes in network usually arranged in series) on a twisted wire pair as an electrical conducting cable. Each node synchronizes its own clock to the in coming clock signal from the twisted wire pair and sends data on another twisted wire pair, often in real time. Each node in these systems is powered by its own local battery, so there is no need to supply power from the recorder.
However, if a portion of the wire pair, a connector pin, node electronics, or a battery fails, all nodes beyond the failed node lose communication to the recorder. Battery failures may be eliminated by providing power via the twisted pair, but faults resulting from connectors, node electronics, or wire pair problems remain. Further, electrical resistance in the cable causes a drop in line voltage as node distance from the recorder increases. Voltage drops in the cable may make it difficult to effectively connect many nodes over a long distance. Moreover, as mentioned above, connectors are other sources of failures. Therefore, from the reliability standpoint, the fewer conductors and connector pins, the better.